Liquid crystalline doristerol-containing organosiloxanes

ABSTRACT

The liquid crystalline organosiloxanes contain per molecule at least one doristeryl group bonded at the 3β position and can be used as right-handed filter materials and optical media.

This application is a 371 of PCT/EP 93/02842 filed on Oct. 14, 1993.

The present invention relates to liquid crystalline organosiloxanescontaining doristeryl radicals, a process for their preparation, theiruse, organosilanes which can be condensed to give organosiloxanescontaining liquid crystalline doristeryl radicals and mixtures ofdoristerol-containing organosiloxanes with other liquid crystallinematerials.

For some optical applications of liquid crystalline materials, such ase.g. in notch filters, it is necessary to have cholesteric phases havinga right-handed helix and cholesteric phases having a left-handed helixin order to be able to reflect both left and right circularly polarizedlight.

For left-handed helical filters, resort is frequently made here ofcholesterol compounds, i.e. steroid compounds, which apart from thechirality have an adequate mesogenicity, i.e. an adequate tendency toform liquid crystalline phases to produce a stable mesophase. The cyclicorganosiloxanes containing cholesteryl radicals disclosed in U.S. Pat.No. 4,410,570 are suitable, for example, for this.

In the production of right-handed helical filters, use was until nowmade of nonsteroidal molecules which have various disadvantages.

From M. L. Tsai, S. H. Chen, S. D. Jacobs, Appl. Phys. Lett., 54, 2395,1989, it is known that modified hydroxypropylcellulose does not haveadequate mesophase stability and polybenzyl glutamates have too low aglass transition point of -25° C. for long-term stability.

The only known sterol whose esters yield a right-handed helix is thecholest-8(14)-en-3β-ol described in U.S. Pat. No. 3,907,406 and U.S.Pat. No. 3,888,892, of the formula 1 ##STR1## abbreviated as doristerolin the following. The compounds described are aliphatic esters, halo orcarbonate derivatives of doristerol which on the one hand only havesmall mesophase widths and on the other hand can only be used atelevated temperature on account of the crystalline state at roomtemperature.

The object of the present invention was to make available right-handedhelical liquid crystalline materials which at room temperature have astable cholesteric phase, make possible a selective reflection ofright-handed polarized light and whose reflection wavelength is largelytemperature-independent. This material should additionally have ahelical twisting power (htp) which is as high as possible, i.e. a hightendency to formhelical screw structures, in order to be able to keepthe proportion of the expensive chiral component low.

The abovementioned objects are achieved by the present invention bymeans of liquid crystalline organosiloxanes which, per molecule, containat least one doristeryl radical bonded via the 3β-position.

The liquid crystalline organosiloxanes according to the invention show alow tendency towards crystallization, a stabilization and broadening ofthe cholesteric phase compared with the known doristerol derivatives andare present in the glass state at room temperature.

The cholesteric phase can be preserved in the glass state by quenchingafter alignment above the glass transition temperature and is stable atroom temperature. The higher glass transition points of the liquidcrystalline organosiloxanes according to the invention in comparisonwith known right-handed helical materials produce a higher stability inthe frozen cholesteric phase at room temperature.

The liquid crystalline organosiloxanes according to the invention havedistinctly wider mesophases than the known low molecular weightdoristeryl compounds. For example, the average values in the liquidcrystalline cyclic organosiloxanes according to the invention are aboutg30*130i, while doristeryl propionate, for example, has values of k80,5n*83, 5i and doristeryl benzoate values of k111n*140.5i.

The liquid crystalline organosiloxanes according to the invention have adistinctly greater htp and thus a better optical power of rotation perdoristeryl radical than the low molecular weight doristeryl derivatives,such that to achieve the same optical effect smaller amounts ofdoristerol compound have to be employed. The cyclic organosiloxanescontaining cholesteryl radicals described in U.S. Pat. No. 4,410,570 donot show a greater htp in comparison to the corresponding low molecularweight cholesterol compounds.

Besides the doristeryl radicals, the liquid crystalline organosiloxanespreferably contain still other mesogenic radicals which make possiblethe subsequent free radical or ionic crosslinking of the right-handedhelical filter.

By altering the content of doristeryl radicals and the ratio ofdoristeryl radicals to other mesogenic radicals in the liquidcrystalline organosiloxanes according to the invention, the reflectionwavelength of the selective reflection can be adjusted. On account ofthe high htp values, only an amount of 10 to 20 mol %, based on allmesogenic radicals present in the organosiloxanes on doristerylradicals, is required in order to obtain a reflection in the visiblerange, while with the corresponding cholesterol-containingorganosiloxanes between 40 and 50 mol % of cholesteryl radicals arerequired.

The doristeryl radicals are preferably bonded to the siloxane structurevia other mesogenic groups. The term "mesogenic groups" is well known inthe field. These are those groups which can produce liquid crystallineproperties in a molecule.

Examples of mesogenic groups are derivatives of cyclohexane, such ascyclohexyl cyclohexylcarboxylates, phenyl cyclohexylcarboxylates,cyclohexylbenzenes, dicyclohexyl derivatives, derivatives of stilbene,phenyl benzoate and its derivatives, steroids, such as cholesterol, itsderivatives, such as cholesterol esters, cholestane and its derivatives,benzylideneanilines, azobenzene and its derivatives, azoxybenzene andits derivatives, alkyl and alkoxyderivatives of biphenyl and Schiff'sbases.

It is often desired for application technology reasons that themesogenic groups contain polar functions, such as, for example, thenitrile group, in order to achieve a high dielectric anisotropic effectin the liquid crystal.

The abovementioned liquid crystalline organosiloxanes are preferablythose which are constructed from at least two units of the generalformula 2

     B.sub.o R.sub.p H.sub.q SiO.sub.(4-o-p-q)/2 !             (2),

in which B is a mesogenic radical of the general formula 3

    R.sup.1 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(--X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i -dor(3),

and optionally a mesogenic radical of the general formula 4

    R.sup.1 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(--X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i --A.sup.5.sub.k                                           ( 4),

where in the above formulae 2, 3 and 4

R is identical or different, optionally substituted C₁ - to C₁₈-hydrocarbon radicals,

o is an integer of value 0 to 3,

p is an integer of value 0 to 3 and an average value of 0.8 to 2.2,

q is an integer of value 0 to 3 and the sum of o, p and q is at most 3,

R¹ is a radical of the formula C_(n) H_(m) in which

n is an integer of value 1 to 20,

m has the value 2n, or if n is at least 2, can also have the value(2n-2), and in R¹ one or more methylene units can be replaced by oxygenatoms which can be bonded to carbon and/or silicon atoms,

X¹ and X² are identical or different bivalent radicals from the groupconsisting of --O--, --COO--, --CONH--, --CO--, --S--, --C.tbd.C--,--CH═CH--, --CH═N--, --CH₂ CH₂ --, --N═N-- and --N═N(O)--,

A¹, A², A³ and A⁴ are identical or different bivalent radicals, namely1,4-phenylene or 1,4-cyclohexylene radicals, substituted arylenes having6 to 10 carbon atoms, substituted cycloalkylenes having 6 to 10 carbonatoms and heteroarylenes having 1 to 10 carbon atoms,

Z is identical or different bi- or tetravalent benzene, cyclohexane orcyclopentane radicals,

dor is a doristeryl radical bonded via the 3β-position,

A⁵ is identical or different, saturated or olefinically unsaturatedalkyl, alkoxy or cycloalkyl radicals in each case having 1 to 16 carbonatoms, cholestane radicals, cholesteryl radicals, halogen atoms,hydrogen atoms, hydroxyl, nitrile, acryloxy, (meth)acryloxy,(meth)acryloxyethylenoxy, (meth)acryloxydi(ethylenoxy),(meth)acryloxytri(ethylenoxy) and trialkylsiloxy groups whose alkylradicals in each case have 1 to 8 carbon atoms,

a, b, c, d, f, g, h, i and k in each case are identical or differentintegers of value 0 to 3, the sum a+b+c+d+e+f+g+h+i+k being at least 2and the sum of d and i being at most 4, and

e is an integer of value 0 or 1.

Examples of unsubstituted radicals R are alkyl radicals, such as themethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl,n-pentyl, isopentyl, neopentyl or tert-pentyl radical, hexyl radicals,such as the n-hexyl radical, heptyl radicals, such as the n-heptylradical, octyl radicals, such as the n-octyl radical and isooctylradicals, such as the 2,2,4-trimethylpentyl radical, nonyl radicals,such as the n-nonyl radical, decyl radicals, such as the n-decylradical, dodecyl radicals, such as the n-dodecyl radical, octadecylradicals, such as the n-octadecyl radical; alkenyl radicals, such as thevinyl radical and the allyl radical; cycloalkyl radicals, such ascyclopentyl, cyclohexyl or cycloheptyl radicals and methylcyclohexylradicals; aryl radicals, such as the phenyl, naphthyl, anthryl andphenanthryl radicals; alkaryl radicals, such as o-, m- or p-tolylradicals, xylyl radicals and ethylphenyl radicals; aralkyl radicals,such as the benzyl radical, the α- and the β-phenylethyl radical;

Examples of substituted radicals R are cyanoalkyl radicals, such as theβ-cyanoethyl radical, and halogenated hydrocarbon radicals, for examplehaloalkyl radicals, such as the 3,3,3-trifluoro-n-propyl radical, the2,2,2,2',2',2'-hexafluoroisopropyl radical and the heptafluoroisopropylradical, and haloaryl radicals, such as the o-, m- and p-chlorophenylradical. R in each case is preferably an optionally halogenatedhydrocarbon radical having 1 to 18, in particular 1 to 10, carbon atoms.

Radicals R which are particularly preferred are C₁ - to C₄ -alkylradicals and phenyl radicals, in particular methyl radicals.

The radicals X¹ and X², if they are not symmetrically constructed, canbe bonded to each of their binding partners by each of their ends. Thus,for example, in the above formulae 3 and 4 and in the formulae below theradical --COO-- can also be bonded as --OOC--, the radical --CONH-- canalso be bonded as --NHCO--, and --CH═N-- can also be bonded as --N═CH--.

Substituents which are preferred for the substituted arylenes andcycloalkylenes A¹, A², A³ and A⁴ are halogen atoms, C₁ - to C₄ -alkoxyradicals, nitro and cyano groups, C₁ - to C₆ -alkyl radicals,carboxy-(C₁ - to C₄ -alkyl) radicals and tri-(C₁ - to C₄ -alkyl)-siloxyradicals.

Preferably, n in R¹ has a value of 3 to 6 and m preferably has the value2n.

Examples of radicals A⁵ are alkyl radicals, such as the methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl,neopentyl or tert-pentyl radical, hexyl radicals, such as the n-hexylradical, heptyl radicals, such as the n-heptyl radical, octyl radicals,such as the n-octyl radical and isooctyl radicals, such as the2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonylradical, decyl radicals, such as the n-decyl radical, dodecyl radicals,such as the n-dodecyl radical, hexadecyl radicals, such as then-hexadecyl radical; alkenyl radicals, such as the vinyl and the allylradicals, butenyl, pentenyl, hexenyl, heptenyl, octenyl, octadienyl,decenyl, dodecenyl and hexadecenyl radicals; cycloalkyl radicals, suchas cyclopentyl, cyclohexyl or cycloheptyl radicals and methylcyclohexylradicals; alkoxy radicals, such as the methoxy, ethoxy, n-propoxy,isopropoxy, n-, sec- and tert-butoxyradicals, pentoxy, hexoxy, octoxy,decoxy- and hexadecoxy radicals; alkenoxy radicals, such as the allyloxyradical, butenyloxy, pentenyloxy, hexenyloxy, octenyioxy, decenyloxy andhexadecenyloxy radicals; cycloalkyl radicals, such as the cyclopentyl,cyclohexyl or cycloheptyl, radical; cycloalkenyl radicals, such ascyclopentenyl, cyclohexenyl and cycloheptenyl radicals; cholestaneradicals; the cholesteryl radical; fluorine, chlorine or bromine atoms;hydrogen atoms; hydroxyl, nitrile and trimethylsilyl or triethylsilylgroups. It is very particularly preferred that --R¹ --(X¹ _(a) --A¹ _(b)--A² _(c))_(d) -- in the abovementioned formulae 3 and 4 is a radical ofthe formula 11 ##STR2##

Radicals of the formulae 3 and 4 which are particularly preferred arethose of the general formulae 12 and 13 ##STR3## in which X², A³, A⁵, f,g and k have the meanings indicated for formulae 3 and 4 and fpreferably has the value 1, g either 0 or 1 and k the value 1.

The liquid crystalline organosiloxanes according to the invention can beprepared by reaction of organosiloxanes and/or organosilanes which canbe condensed to give organosiloxanes with alkenes or alkynes containingmesogenic groups, the organosiloxanes and at least some of theorganosilanes having at least one hydrogen atom bonded directly tosilicon.

In a preferred process for the preparation of liquid crystallineorganosiloxanes of the above general formula 2, in which n in themesogenic radicals of the general formulae 3 and 4 is an integer ofvalue 2 to 20, organosiloxanes which are constructed from units of thegeneral formula 14

     R.sub.p H.sub.q+o SiO.sub.(4-o-p-q)/2 !                   (14)

and/or organosilanes of the general formula 15

    R.sub.r H.sub.s+o SiY.sub.(4-o-r-s)/2                      ( 15)

are reacted with mesogenic compounds of the general formula 16

    R.sup.2 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(--X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i -dor(16)

and optionally mesogenic compounds of the general formula 17

    R.sup.2 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(--X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i --A.sup.5.sub.k                                           ( 17)

and, if organosilanes of the general formula 15 are employed, theorganosilanes obtained of the general formula 18

    B.sub.o R.sub.r H.sub.s SiY.sub.(4-o-r-s)/2                ( 18)

are condensed,

where in the above formulae 14 to 18

Y is a condensable group,

R² is a radical of the formula C_(n) H_(m), in which

m has the value 2n-1 or 2n-3,

r and s in each case are an integer of value 0 to 3, the sum of o, r ands is at most 3, and o, p, q, X¹, X², A¹, A², A³, A⁴, A⁵, a, b, c, d, e,f, g, h, i, k, Z, dor, B and R have the meaning indicated for thegeneral formulae 2, 3 and 4.

Y is preferably a halogen atom or a C₁ - to C₄ -alkoxy group, inparticular a chlorine atom or a methoxy or ethoxy group. The value of sis preferably 0 or 1.

In the above general formulae 16 and 17, n in R² preferably has a valueof 3 to 6 and m preferably has the value 2n-1.

The reaction of organosiloxanes containing hydrogen atoms bondeddirectly to silicon and/or organosilanes which can be condensed to giveorganosiloxanes with alkenes or alkynes containing mesogenic groups iscarried out in a manner known per se, e.g. by hydrosilylation insolvents, such as hydrocarbons, ethers or esters using metals orcompounds of the platinum group as catalyst. Suitable processes forhydrosilylation are described, for example, in EP-A-466 183 and in J.Kupfer, H. Finkelmann; Makromol. Chem., Rapid Commun. 12,717, 1991.

For the preparation of liquid crystalline organosiloxanes according tothe invention which contain 4 methacryloxy and/or acryloxy groups in themesogenic radicals of the general formula 4, the process described inEP-A-358 208 is preferred.

0.1 to 10 mol, in particular 0.5 to 2 mol, of compounds of the formulae3 and 4 are preferably employed per gram atom of hydrogen atoms bondeddirectly to silicon atoms in the hydrosilylation.

Siloxanes of the formula (14) which are particularly preferred are thosewhich are constructed to at least 90% of their units from those of theformulae 5 to 10

     (CH.sub.3).sub.2 SiO!,                                    (5)

     (CH.sub.3)HSiO!,                                          (6)

     H.sub.2 SiO!,                                             (7)

     H(CH.sub.3).sub.2 SiO.sub.1/2 !,                          (8)

     (CH.sub.3).sub.3 SiO.sub.1/2 !                            (9)

    and

     HSiO.sub.3/2 !                                            (10)

and contain 2 to 100 silicon atoms per molecule, in particular 2 to 15silicon atoms per molecule.

If, in the process described above, organosilanes, for example of thegeneral formula 15, are employed, these are condensed together withorganosilanes or organosiloxanes containing doristeryl radicals to giveliquid crystalline organosiloxanes by processes known per se. This canbe carried out, inter alia, by reaction with acids, such as aqueoushydrochloric acid. Processes of this type are described in W. Noll:Chemistry and Technology of Silicones, Academic Press, Orlando Fla.,1968, page 191 to 239.

A mixture of different molecules is obtained by means of the reactionsdescribed above.

The novel organosilanes of the above general formula 18, in which odenotes an integer of value 1, 2 or 3, are likewise the subject of thepresent invention as intermediates for the preparation of the liquidcrystalline organosiloxanes.

The doristerol-containing organosiloxanes according to the invention canbe used in various ways in optical elements and as polarizing colorfilters, in particular notch filters. They allow the right-handedpolarized portion of the light to be reflected in certain prespecifiedspectral ranges.

Both mixtures of the organosiloxanes according to the invention with oneanother and mixtures of the organosiloxanes according to the inventionwith other liquid crystalline materials or pure doristerol-containingorganosiloxanes can be used for the above application. In particular,mixtures with other liquid crystalline substances, specifically alsowith left-handed helical materials, can also be used, by means of whicha tuning of the reflection wavelength between 400 nm right-handedhelical through infrared right-handed helical, nematic (=infinitepitch), infrared left-handed helical to 400 nm left-handed helical canbe carried out.

The mixtures of the liquid crystalline organosiloxanes with one anotherand with other liquid crystalline materials are likewise a subject ofthe present invention.

The liquid crystalline organosiloxanes according to the invention, whichhave methacryloxy and/or acryloxy groups in the mesogenic radicals ofthe general formula 4, can be three-dimensionally crosslinked. Thiscrosslinking is preferably effected by means of free radicals, which areproduced by peroxides, by UV light or by more energy-richelectromagnetic radiation than UV light, or thermally. The crosslinking,however, can also be effected by means of crosslinkers containinghydrogen atoms bonded directly to silicon atoms with catalysis by theabovementioned platinum metal catalysts. It can also be carried outcationically or anionically. Crosslinking by UV light is particularlypreferred. This crosslinking is described in EP-A-358 208.

In the following examples, if not indicated otherwise in each case,

a) all quantitative data are based on the weight;

b) all pressures are 0.10 MPa (abs.);

c) all temperatures are 20° C.;

d) htp=helical twisting power;

e) n*=cholesteric;

f) g=glass;

g) k=crystalline;

h) i=isotropic.

EXAMPLE 1

a) Preparation of doristeryl 4-(propen-2-oxy)benzoate

50 g of cholestadiene were dissolved in 800 ml of dry ethyl acetate towhich 30 ml of acetic acid had previously been added and after additionof 1.5 g of platinum oxide the mixture was transferred to an autoclaveof 2 1 volume. Hydrogenation was carried out at 50° C. and 10 atmhydrogen pressure and was complete after 24 h. After reaction wascomplete, the catalyst was filtered off, the solvent was concentrated ina rotary evaporator and the doristerol obtained was recrystallized fromethanol. Yield: 42.5 g (88.5%). The purity of the substance wasconfirmed with the aid of ¹ H-NMR and ¹³ C-NMR spectroscopy. 17 g of4-(propen-2-oxy)benzoyl chloride and 32 g of doristerol were dissolvedin 200 ml of dry toluene and heated to reflux for 15 h. The solvent wasthen distilled off and the residue was recrystallized from ethanol;yield: 44.9 g (99%), m.p. 92° C. (n*105i).

b) Hydrosilylation

1 g of doristeryl 4-(propen-2-oxy)benzoate, 1.53 g of 4'-phenylphenyl4-(propen-2-oxy)benzoate and 646 mg of pentamethylcyclopentasiloxanewere dissolved in 20 ml of dry toluene and, after addition of 0.1 ml ofa solution of dicyclopentadienylplatinumdichloride (1% by weight inmethylene chloride), heated at 100° C. for 1 h. 1.45 g of(4-methacryloxy)phenyl 4-(propen-2-oxy)benzoate, 500 ppm of hydroquinoneand a further 0.1 ml of the catalyst solution were added to the solutioncooled to 50° C.; this solution was stirred at 70°-80° C. for half anhour. After reaction was complete, the catalyst was removed by means ofa short column packed with silica gel (1=3 cm, diameter=3 cm) and theproduct was precipitated in ethanol. 2.8 g (60%) of a substance having areflection wavelength of 456 nm--corresponding to an htp of 15.7 μm⁻¹--were obtained. The substance had a glass transition point at 27° C.and a clear point at 126° C.

EXAMPLE 2

1 g of doristeryl 4-(propen-2-oxy)benzoate, 1.81 g of 4'-phenylphenyl4-(propen-2-oxy)benzoate and 733 mg of pentamethylcyclopentasiloxanewere dissolved in 20 ml of dry toluene and, after addition of 0.1 ml ofa solution of dicyclopentadienylplatinum dichloride (1% by weight inmethylene chloride), the mixture was heated at 100° C. for 1 h. 1.65 gof (4-methacryloxy)phenyl 4-(propen-2-oxy)benzoate, 500 ppm ofhydroquinone and a further 0.1 ml of the catalyst solution were added tothe solution cooled to 50° C.; this solution was stirred at 70°-80° C.for half an hour. After reaction was complete, the catalyst was removedby means of a short column packed with silica gel (1=3 cm, diameter=3cm) and the product was precipitated in ethanol. 2.4 g (46%) of asubstance having a reflection wavelength of 500 nm--corresponding to anhtp of 16.1 μm⁻¹ --were obtained. The substance had a glass transitionpoint at 31° C. and a clear point at 136° C.

EXAMPLE 3

1 g of doristeryl 4-(propen-2-oxy)benzoate, 2.69 g of 4'-phenylphenyl4-(propen-2-oxy)benzoate and 1 g of pentamethylcyclopentasiloxane weredissolved in 20 ml of dry toluene and, after addition of 0.1 ml of asolution of dicyclopentadienylplatinum dichloride (1% by weight inmethylene chloride), the mixture was heated at 100° C. for 1 h. 2.25 gof (4-methacryloxy)phenyl 4-(propen-2-oxy)benzoate, 500 ppm ofhydroquinone and a further 0.1 ml of the catalyst solution were added tothe solution cooled to 50° C.; this solution was stirred at 70°-80° C.for half an hour. After reaction was complete, the catalyst was removedby means of a short column packed with silica gel (1=3 cm, diemeter=3cm) and the product was precipitated in ethanol. 3.8 g (55%) of asubstance having a reflection wavelength of 681 nm--corresponding to anhtp of 15.8 μm⁻¹ --were obtained. The substance has a glass transitionpoint at 23° C. and a clear point at 122° C.

EXAMPLE 4

a) Doristeryl 2-(propen-2-oxy)-6-naphthalenecarboxylate

3.2 g of 2-(propen-2-oxy)-6-naphthalenecarboxyl chloride and 5 g ofdoristerol were dissolved in 40 ml of dry toluene and heated to refluxfor 6 h. The crude product was concentrated in a rotary evaporator andrecrystallized from ethanol; yield 5.6 g (73%), m.p. 105° C. (n*132i).

b) Hydrosilylation

2 g of doristeryl 2-(propen-2-oxy)-6-naphthalenecarboxylate, 2.22 g of4'-phenylphenyl 4-(propen-2-oxy)benzoate and 1 g ofpentamethylcyclopentasiloxane were dissolved in 20 ml of dry tolueneand, after addition of 0.1 ml of a solution ofdicyclopentadienyl-platinum dichloride (1% by weight in methylenechloride), the mixture was heated at 100° C. for 1 h. 2.27 g of(4-methacryloxy)phenyl 4-(propen-2-oxy)benzoate, 500 ppm of hydroquinoneand a further 0.1 ml of the catalyst solution were added to the solutioncooled to 50° C.; this solution was stirred at 70°-80° C. for half anhour. After reaction was complete, the catalyst was removed by means ofa short column packed with silica gel (1=3 cm, diameter=3 cm) and theproduct was precipitated in ethanol. 4.9 g (65%) of a substance having areflection wavelength of 522 nm--corresponding to an htp of 13.4 μm⁻¹--were obtained. The substance had a glass transition point at 53° C.and a clear point at 147° C.

EXAMPLE 5

The doristerol-containing organosiloxane having a reflection wavelengthof 456 run prepared according to Example 1 was mixed in certain weightratios with an appropriate cholesterol-containing organosiloxane havinga reflection wavelength of 555 nm. The proportions by weight andreflection wavelengths of the mixtures are to be taken from thefollowing table.

                  TABLE 1                                                         ______________________________________                                        Doristerol-                                                                             Cholesterol-                                                        containing                                                                              containing   Reflection                                                                             Handedness                                    siloxane/%                                                                              siloxane/%   wave-    of the helix                                  by weight by weight    length/nm                                                                              r/l                                           ______________________________________                                        100       0            456      r                                             96.1      3.9          506      r                                             88.8      11.2         628      r                                             77.6      22.4         884      r                                             64.3      35.7         1891     r                                             34.5      65.5         1310     l                                             21.9      78.1         838      l                                             13.1      86.9         683      l                                             4.1       95.9         583      l                                             0         100          555      l                                             ______________________________________                                    

Comparison Example 6

The htp values of low molecular weight doristerol compounds weremeasured by admixing in Merck-Nematen® ZLI-1565 and measuring theGrandjean-Cano disclination lines in a wedge cell. Doristerol has an htpof 8-9 μm⁻¹, doristeryl 4-(propen-2-oxy)benzoate an htp of 5 μm⁻¹.

We claim:
 1. A liquid crystalline organosiloxane which contains at leastone doristeryl radical bonded via the 3β-position per moleculecomprising at least two units of the general formula 2

     B.sub.o R.sub.p H.sub.q SiO.sub.(4-o-p-q)/2 !             (2),

in which B is a mesogenic radical of the general formula 3

    R.sup.1 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i -dor(3),

and optionally a mesogenic radical of the general formula 4

    R.sup.1 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i --A.sup.5.sub.k( 4),

where in the above formulae 2, 3 and 4 R is an identical or different,optionally substituted C₁ - to C₁₈ -hydrocarbon radical, o is an integerof value 0 to 3, p is an integer of value 0 to 3 q is an integer ofvalue 0 to 3 and the sum of o, p and q is at most 3, R¹ is a radical ofthe formula C_(n) H_(m) in which n is an integer of value 2 to 20, m hasthe value 2n, or if n is at least 2, can also have the value (2n-2), andin R¹ one or more methylene units can be replaced by oxygen atoms whichcan be bonded to carbon and/or silicon atoms, X¹ and X² are identical ordifferent bivalent radicals from the group consisting of --O--, --COO--,--CONH--, --CO--, --S--, --C.tbd.C--, --CH═CH--, --CH═N--, CH₂ CH₂ --,--N═N-- and --N═N(O)--, A¹, A², A³ and A⁴ are identical or differentbivalent radicals, selected from the group consisting of 1,4-phenylleneor 1,4-cyclohexylene radicals, substituted arylenes having 6 to 10carbon atoms, and substituted cycloalkylenes having 6 to 10 carbonatoms, Z is identical or different bi- or tetravalent benzene,cyclohexane or cyclopentane radicals, dor is a doristeryl radical bondedvia the 3β-position, A⁵ is identical or different, saturated orolefinically unsaturated alkyl, alkoxy or cycloalkyl radicals in eachcase having 1 to 16 carbon atoms, cholestane radicals, cholesterylradicals, halogen atoms, hydrogen atoms, hydroxyl, nitrile, acryloxy,(meth)acryloxy, (meth)acryloxyethylenoxy, (meth)acryloxydi(ethylenoxy),(meth)acryloxytri(ethylenoxy) and trialkylsiloxy groups whose alkylradicals in each case have 1 to 8 carbon atoms, a, b, c, d, f, g, h, iand k in each case are identical or different integers of value 0 to 3,the sum a+b+c+d+e+f+g+h+i+k being at least 2 and the sum of d and ibeing at most 4, and e is an integer of value 0 or
 1. 2. A process forthe preparation of liquid crystalline organosiloxanes as claimed inclaim 1, in which n in the mesogenic radicals of formulae 3 and 4 is aninteger of value 2 to 20, which comprises reacting organosiloxanescomprising units of the formula

     R.sub.p H.sub.q+o SiO.sub.(4-o-p-q)/2 !                   (14)

and/or organosilanes of the formula

    R.sub.r H.sub.s+o SiY.sub.(4-o-r-s)/2                      ( 15)

with mesogenic compounds of the formula

    R.sup.2 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(--X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i -dor (16)

and optionally mesogenic compounds of the formula

    R.sup.2 --(X.sup.1.sub.a --A.sup.1.sub.b --A.sup.2.sub.c).sub.d --Z.sub.e --(--X.sup.2.sub.f --A.sup.3.sub.g --A.sup.4.sub.h --).sub.i --A.sup.5.sub.k                                           ( 17)

and, if organosilanes of formula 15 are present, condensing theorganosilanes obtained of the formula

    B.sub.o R.sub.f H.sub.s SiY.sub.(4-o-r-s)/2                ( 18)

where in the above formulae 14 to 18 Y is a condensable group, R² is aradical of the formula C_(n) H_(m), in which m has the value 2n-1 or2n-3, r and s are an integer of value 0 to 3, the sum of o, r and s isat most 3, and o, p, q, X¹, X², A¹, A², A³, A⁴, A⁵, a, b, c, d, e, f, g,h, i, k, Z, dor, B and R have the meaning indicated in claim
 1. 3. Aliquid crystalline organosiloxane as claimed in claim 1 comprising amixture of a liquid crystalline organosiloxane having at least onedoristeryl radical bonded via the 3β-position and other liquidcrystalline materials and optionally left-handed helical cholestericmaterials.
 4. A process for the preparation of liquid crystallineorganosiloxanes as claimed in claim 2 containing organosilanes of thegeneral formula 18, where o is an integer having a value of 1, 2 or 3.5. An optical filter material containing a liquid crystallineorganosiloxane as claimed in claim 1.